2. How could ancient astronomers know that the sun was in a particular zodiac constellation, even though stars other than the sun are not visible in the daytime?

The correct answer to this open question is the following.

Ancient astronomers could know that the sun was in a particular zodiac constellation, even though stars other than the sun are not visible in the daytime for the following reason.

When we talk about ancient astronomers we are referring to the Sumerian astronomers. The Sumerians were great astronomers and astrologers approximately 5,500 years ago. They understood the sky and the zodiac. The Babylonian priests studied the sky and the constellations and believed that these influenced the events on Earth. They realized that constellations disappeared and appeared with the changes of seasons. They based their observations on the night sky and the idea of the Earth orbited the Sun in a plane orbit called Ecliptic Plane. That is how ancient astronomers from Mesopotamia determined that during the day, the Sun gives the impression of passing through the constellations throughout the year. So, since is the perception on Earth, they believed that not only the Sun but other planets and the Moon passed through the twelve constellations.